The present invention relates to a diesel piston engine of a novel type, at least one cylinder of which may be used, as desired, sometimes as an engine cylinder, and at other times as an air compressor cylinder. Such a device is provided, more particularly, though not exclusively, for the diesel engine of a vehicle, such as a truck or a bus.
It is known that in vehicles of this type, it is necessary to provide an effect called "braking with the motor" to insure the engine's restraint during the phases of deceleration or during operation on downhill grades. During these deceleration phases, the driver operates the braking system, which in heavy trucks is precisely the main consumer of compressed air. This compressed air is generally supplied by an auxiliary pistion compressor which is mechanically coupled with the motor. It is clear that, apart from the periods when this compressor is delivering compressed air to the braking system for decleration, that is, most of the time, the energy consumed for keeping the compressor rotating is wasted and therefore decreases the efficiency of the vehicle.
An attempt has been made to improve this situation by incorporating into the engine one or more cylinders capable of insuring the operation of the compressor, or at least, an operation increasing the effect of braking with the motor.
A first solution, described for example in U.S. Pat. No. 1,804,873, consists in using a single cylinder block in which certain cylinders are engine cylinders, while others operate as a compressor. The disadvantages of this system are twofold. The compressor cylinders are specialized and may never be used as engine cylinders. Furthermore, a loss of energy exists due to rotation of the mobile coupling of the compressor cylinders, even when this is not necessary.
Another solution, described for example in U.S. Pat. No. 3,365,014, consists in provisionally modifying the distribution principle in only certain cylinders of a diesel motor, the operation of which may at will be either that of an engine cylinder or a compressor cylinder. The disadvantage of prior art engines of this type is that the cylinders are identical to one another. Thus the output obtained is very mediocre when operating as compressor or for restraining the vehicle. Moreover, it is found that, although this system makes it possible to restrain the vehicle in going downhill, it is insufficient to constitute a real source of compressed air, and particularly is insufficient to adequately refill the compressed air storage cylinders.